1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a base plate for attaching a head suspension assembly to a head actuator arm.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write data to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body. The suspensions include a flexible load beam constructed of light sheet steel that has a bend formed in it. The load beam acts as a spring that forces the head against the disk surface with an accurate pre-load or xe2x80x9cgram loadxe2x80x9d. Air turbulence caused by the rotating disks lifts the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces. The air bearing force is counteracted by the suspension gram load.
The head suspension is attached to an actuator arm using a base plate that forms a part of the head suspension. The base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam clearance hole and the flange is spot welded to the load beam. Alternatively, the hub and load beam clearance hole are aligned and the flange is welded on the opposite side. The combined base plate, load beam and a flexure make up the head suspension, and the suspension has the hub of the base plate extending beyond the load beam and concentric with the clearance hole.
The hubs of the suspensions are inserted into actuator arm boss holes formed through actuator arms extending from an actuator body. In the middle actuator arms, the hubs of two suspensions enter the arm boss hole from each end of the hole, so that the transducer heads of the suspensions face in opposing directions. A swage ball is passed through the concentric cylindrical hubs and boss holes to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss holes.
Problems with this method of mounting transducer heads have arisen as the need for increased data storage capacity in hard disk drives has grown and the size of the disk drive has decreased to fit in small lap top computers. The problem of forming a strong connection between the actuator arms and the transducer suspensions has been made more difficult as the size of the components has become smaller. In the prior art, relatively high swaging forces are needed to insure that a base plate makes a strong connection with the actuator arm boss hole. As the part get smaller and thinner, these high forces cause unacceptable large distortions in the load beam and pre-load changes.
It is therefore an object of this invention to provide a base plate that reduces pre-load change caused by the swaging process.
Briefly, the invention is concerned with a base plate for fitting into a boss hole of a predetermined nominal diameter. The base plate comprises a flange and a hub extending from a region at which the hub meets the flange to an outer end of the hub. The hub has a number of arcuate indentations in the hub extending from the outer end of the hub part way or all the way to the region at which the hub meets the flange. The base plate can be used in a swaging operation or in a press-in operation. During a swaging operation the indentations amplify the expansion forces from the swage tool to engage the boss hole and can achieve snap-through shape change for permanent locking. For a press-in fit the diameter of the hub is greater than the nominal diameter.
The invention has the advantage that the unique base plate geometry increases outward boss expansion and decreases required swage force and associated gram load changing drag down.
The invention has the advantage that gram load change inherent in swaging is reduced and a large retention torque can be created even in a low hub height configurations that offer limited retention torque in a standard hub geometry.
The invention also has the advantage that the base plate reduces the large stresses and deformations associated with high swaging forces that result in gram load change.